Blood collection tube assembly

ABSTRACT

The present invention is a plastic container coated with a multi-layer barrier coating. The multi-layer barrier coating is useful for providing an effective barrier against gas permeability in containers and for extending shelf-life of containers, especially plastic evacuated blood collection devices.

This is a divisional of co-pending application Ser. No. 08/594,069,filed Jan. 30, 1996 now U.S. Pat. No. 5,716,683.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a multi-layer barrier coating for providing aneffective barrier against gas and water permeability for containers,especially plastic blood collection tubes.

2. Description of the Related Art

With the increased emphasis on the use of plastic medical products, aspecial need exists for improving the barrier properties of articlesmade of polymers.

Such medical products that would derive a considerable benefit fromimproving their barrier properties include, but are not limited to,collection tubes and particularly those used for blood collection.

Blood collection tubes require certain performance standards to beacceptable for use in medical applications. Such performance standardsinclude the ability to maintain greater than about 90% original drawvolume over a one year period, to be radiation sterilizable and to benon-interfering in tests and analysis.

Therefore, a need exists to improve the barrier properties of articlesmade of polymers and in particular plastic evacuated blood collectiontubes wherein certain performance standards would be met and the articlewould be effective and usable in medical applications.

SUMMARY OF THE INVENTION

The present invention is a plastic composite container with amulti-layer barrier coating comprising at least two barrier materialsdisposed over the outer or inner surface of the previously formedcomposite container. Desirably, the barrier materials comprise a firstlayer of a polymeric material applied to the outer surface of thepreviously formed composite container, a second layer of an inorganicmaterial applied over the first layer and optionally a third layer oforganic material applied over the second layer.

The first layer, a primer coating, is preferably a heterocyclic compoundsuch as ethylene oxides. This type of compound is frequently called anepoxide, although the formal IUPAC nomenclature is oxirane. The coatingmay be formed either on an interior surface portion, on an exteriorsurface portion, or both of the container.

The second layer of the barrier coating may preferably be a siliconoxide based composition, such as SiO_(x) wherein x is from 1.0 to about2.5; or an aluminium oxide based composition. Most preferably, thesecond layer is a silicon oxide based composition applied over the firstlayer.

The optional third layer of the barrier coating preferably an organicbarrier composition, such as poly (vinylidene chloride) (PVDC), is mostpreferably applied over the second layer.

Desirably, the primer coating is formed by an application of an uncuredpolyamine polyepoxide mixture, followed by exposure Lo a photolytic orthermal curing source.

Preferably, the primer coating is a highly cross-likedpolyarmine/polyepoxide mixture as described in International Patent WO93/07068 and U.S. Pat. No. 4,478,874, the disclosures of which areherein incorporated by reference.

Preferably, the thickness of the epoxide primer coating is about 100microns to about 300 microns and most preferably from about 100 micronsto about 175 microns.

A desirable second layer which is disposed over the first layerpreferably comprises a silicon oxide based composition, such as SiO_(x).Such a film desirably is derived from volatile organosilicon compounds.

The silicon oxide based composition provides a dense, vapor-imperviouscoating over the primer organic coating. Preferably, the thickness ofthe silicon oxide based layer is about 100 to about 2,000 Angstroms (Å)and most preferably from about 500 to about 1,000 Å. A coating above5,000 Å may crack and therefore be ineffective as a barrier.

A desirable optional third layer which is disposed over the second layerpreferably comprises vinylidene chloride--methylmethacrylate--methacrylate acrylic acid polymer (PVDC), thermosettingepoxy coatings, parylene polymers or polyesters.

Preferably, the thickness of the PVDC layer is about 2 to about 15microns and most preferably from about 3 to about 5 microns.

The process for applying the primer coating to a container is preferablycarried out as described in International Publication No. 93/07068 andU.S. Pat. No. 4,478,874 wherein said mixture is coated into a bloodcollection tube and cured by thermal methods. The deposition and curingsteps may be repeated until the desired number of layers has beenachieved.

A method for depositing a silicon oxide based film is as follows: (a)pretreating the first layer on the container with a first plasma coatingof oxygen; (b) controllably flowing a gas stream including anorganosilicon compound into a plasma; and (c) depositing a silicon oxideonto the first layer while maintaining a pressure of less than about 500mm. H_(g) during the depositing.

Although the pretreatment step is optional, it is believed that thepretreatment step provides for improved adherence qualities between thesecond layer and the primer coating.

The organosilicon compound is preferably combined with oxygen andoptionally helium or another inert gas such as argon or nitrogen and atleast a portion of the plasma is preferably magnetically confinedadjacent to the surface of the first layer during the depositing, mostpreferably by an unbalanced magnetron.

The PVDC layer may be applied over the second layer by dipping orspraying techniques.

Most preferably, the method for depositing a barrier coating on asubstrate, such as a plastic collection tube comprises the followingsteps:

(a) applying an uncured polyamine polyepoxide mixture onto the outersurface of a container;

(b) curing said mixture;

(c) vaporizing an organosilicon component and admixing the volatilizedorganosilicon component with an oxidizer component and optionally aninert gas component to form a gas steam exterior to the chamber;

(d) establishing a glow discharge plasma in the chamber from one or moreof the gas stream components;

(e) controllably flowing the gas stream into the plasma while confiningat least a portion of the plasma therein; and

(f) depositing a second layer of a silicon oxide coating adjacent saidfirst layer.

Optionally, a PVDC coating may be applied over the second layer bydipping or spraying techniques. An emulsion based PVDC solution may beused for dipping the container surface, followed by thermal curing.Solvent based PVDC solutions, where the solvent is CHCl₃, CCl₄ and thelike, may be used for spray-coating, followed by thermal curing.

Optionally, the container and/or the first layer may be flame-treated orplasma oxygen treated or corona discharge treated prior to applying themulti-layer coatings.

Plastic tubes coated with the multi-layer barrier coating, comprisingthe primer coating, and an oxide layer and an overcoating layer are ableto maintain substantially far better vacuum retention, draw volume andthermomechanical integrity retention than previous tubes comprised ofpolymer compositions and blends thereof without a coating of barriermaterials or of tubes comprising only an oxide coating. In addition, thetube's resistance to impact is much better than that of glass. Mostnotably is the clarity of the multi-layer coating and its durability tosubstantially withstand resistance to impact and abrasion.

Most preferably, the container of the present invention is a bloodcollection device. The blood collection device can be either anevacuated blood collection tube or a non-evacuated blood collectiontube. The blood collection tube is desirably made of polyethyleneterephthalate, polypropylene, polyethylene napthalate or copolymersthereof.

Printing may be placed on the multi-layer barrier coating applied to thecontainer of interest. For example, a product identification, bar code,brand name, company logo, lot number, expiration date and other data andinformation may all be included on the barrier coating. Moreover, amatte finish or a corona discharged surface may be developed on thebarrier coating so as to make the surface appropriate for writingadditional information on the label. Furthermore, a pressure sensitiveadhesive label may be placed over the barrier coating so as toaccommodate various hospital over-labels, for example.

Preferably, the multi-layer barrier coating of the present inventionprovides a transparent or colorless appearance and may have printedmatter applied thereon.

A further advantage is that the method of the present invention providesa reduction in the gas permeability of three-dimensional objects thathas not been achieved with conventional deposition method typically usedwith thin films.

It has been found in the present invention that the organic material,epoxide provides a good platform for the growth of the dense SiO_(x)barrier material.

It has been found that the epoxide layer improves the adhesion between aplastic surface and SiO_(x) and overall improves the thermomechanicalstability of the coated system. In addition, acrylate primer coating hasa role of a planarization (leveling) layer, covering the particles andimperfections on the surface of a polymer and reducing the defectdensity in the deposited inorganic coatings. The good bonding propertiesof the acrylate are also due to the fact that acrylate is polar and thepolarity provides means for good bond formation between the SiO_(x) andthe acrylate. In addition, it has been found that a good bond formationis made between plastic tubes made of polypropylene and acrylate. Thus,the present invention provides the means of substantially improving thebarrier properties of polypropylene tubes. The adhesion properties ofboth the acrylate coating and the oxide coating can be furthersubstantially improved by surface pretreatment methods such as flame oroxygen plasma. Therefore, a significant reduction in permeability of thearticle is due to the substantially improved SiO_(x) surface coveragethat is obtained by the use of a primer coating of acrylate on theplastic article surface.

The layer of PVDC improves the layer of SiO_(x) because it plugs thedefects and/or irregularities in the SiO_(x) layer. Furthermore, thePVDC layer improves the abrasion resistance of the SiO_(x) layer.

A plastic blood collection tube coated with the multi-layer barriercoating of the present invention will not interfere with testing andanalysis that is typically performed on blood in a tube. Such testsinclude but are not limited to, routine chemical analysis, biologicalinertness, hematology, blood chemistry, blood typing, toxicologyanalysis or therapeutic drug monitoring and other clinical testsinvolving body fluids. Furthermore, a plastic blood collection tubecoated with the barrier coating is capable of being subjected toautomated machinery such as centrifuges and may be exposed to certainlevels of radiation in the sterilization process with substantially nochange in optical or mechanical and functional properties.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a typical blood collection tube with astopper.

FIG. 2 is a longitudinal sectional view of the tube of FIG. 1 takenalong line 2--2.

FIG. 3 is a longitudinal sectional view of a tube-shaped containersimilar to the tube of FIG. 1 without a stopper, comprising amulti-layer barrier coating.

FIG. 4 is a longitudinal sectional view of a tube-shaped container,similar to the tube of FIG. 1 with a stopper, comprising a multi-layerbarrier coating.

FIG. 5 is a longitudinal sectional view of a further embodiment of theinvention illustrating the tube with a stopper similar to FIG. 1 andwith the multi-layer barrier coating encompassing both the tube andstopper thereof.

FIG. 6 illustrates a plasma deposition system.

FIG. 7 is a general schematic diagram illustrating the layers beingdeposited on a substrate.

DETAILED DESCRIPTION

The present invention may be embodied in other specific forms and is notlimited to any specific embodiment described in detail which is merelyexemplary. Various other modifications will be apparent to and readilymade by those skilled in the art without departing from the scope andspirit of the invention. The scope of the invention will be measured bythe appended claims and their equivalents.

Referring to the drawings in which like reference characters refer tolike parts throughout the several views thereof, FIGS. 1 and 2 show atypical blood collection tube 10, having a sidewall 11 extending from anopen end 16 to a closed end 18 and a stopper 14 which includes a lowerannular portion or skirt 15 which extends into and presses against theinner surface 12 of the sidewall for maintaining stopper 14 in place.

FIG. 2 schematically illustrates that there are three mechanisms for achange in vacuum in a blood collection tube: (A) gas permeation throughthe stopper material; (B) gas permeation through the tube and (C) leakat the stopper tube interface. Therefore, when there is substantially nogas permeation and no leak, there is good vacuum retention and good drawvolume retention.

FIG. 3 shows the preferred embodiment of the invention, a plastic tubecoated with at least two layers of barrier materials. The preferredembodiment includes many components which are substantially identical tothe components of FIGS. 1 and 2. Accordingly, similar componentsperforming similar functions will be numbered identically to thosecomponents of FIGS. 1 and 2, except that a suffix "a" will be used toidentify those components in FIG. 3.

Referring now to FIG. 3, the preferred embodiment of the invention,collection tube assembly 20 comprises a plastic tube 10a, having asidewall 11a extending from an opened end 16a to a closed end 18a. Abarrier coating 25 extends over a substantial portion of the outersurface of the tube with the exception of open end 16a. Barrier coating25 comprises a first layer 26 of a polymer material such as an epoxidematerial and a second layer 27 an inorganic material such as a siliconoxide based composition and a third layer 28 of an organic overcoatinglayer such as PVDC.

FIG. 4 illustrates an alternate embodiment of the invention, whereincollection tube assembly 40 comprises stopper 48 in place for closingopen end 41 of tube 42. As can be seen, sidewall 43 extends from openend 41 to closed end 44 and stopper 48 includes an annular upper portion50 which extends over the top edge of tube 42. Stopper 48 includes alower annular portion or skirt 49 which extends into and presses againstthe inside inner surface 46 of sidewall 43 for maintaining stopper 48 inplace. Also, the stopper has a septum portion 52 for receiving a cannulatherethrough.

Thus, the user, once receiving a container such as that shown in FIG. 4with a sample contained therein, may insert a cannula through septum 52for receiving part or all of the contents in tube 42 to perform varioustests on a sample. Covering a substantial portion of the length of thetube is a multi-layer barrier coating 45. Multi-layer barrier coating 45covers substantially most of the tube with the exception of open end 41thereof. Multi-layer barrier coating 45 comprises a first layer 54 of apolymer material such as an epoxide, a second layer 56 of an inorganicmaterial such as a silicon oxide material and a third layer 57 of anorganic barrier material such as PVDC. FIG. 4 differs from theembodiment in FIG. 3 in that the tube may be evacuated with thesimultaneous placement of stopper 48 therein after the application oflayers 54 and 56 over the tube. Alternatively, the multi-layer barriercoating may be applied to the tube after it has been evacuated.

FIG. 5 shows an additional embodiment of the barrier coating and a tube.The alternate embodiment functions in a similar manner to the embodimentillustrated in FIG. 4. Accordingly, similar components performingsimilar functions will be numbered identically to those components inthe embodiment of FIG. 4, except that a suffix "a" will be used toidentify those components in FIG. 5.

Referring now to FIG. 5, a further embodiment 60 of the inventionwherein multi-layer barrier coating 45a incorporates both upper portion50a of stopper 48a, as well as the entire outer surface of tube 42a.Multi-layer barrier coating 45a includes serrations 62 at the tube,stopper interface. The serrations are registered so that it can bedetermined if the sealed container has been tampered with. Such anembodiment may be utilized, for example, for sealing the container withthe stopper in place. Once a sample has been placed in the tube, thesample cannot be tampered with by removal of the stopper. Additionally,the serrations may be registered so that it can be determined if thesealed container has been tampered with. Such an arrangement may beappropriate, for example, in drug abuse testing, specimen identificationand quality control.

In an alternate embodiment of the invention, multi-layer barrier coating45 is repeatedly or sequentially applied to the inner and/or outersurface of the tube. Preferably, the coating is applied at least twice.

It will be understood by practitioners-in-the-art, that such tubes maycontain reagents in the form of additives or coatings on the inner wallof the tube.

The multi-layer barrier coating forms a substantially clear ortranslucent barrier. Therefore, the contents of a plastic tube with amulti-layer barrier coating comprising at least two layers of barriermaterials are substantially visible to the observer at the same timeidentifying information may be displayed over the multi-layer barriercoating after it is applied to the plastic tube.

The first layer of the multi-layer barrier coating may be formed on thetube by dip-coating, roll-coating or spray-coating ethylene oxide oroxirane monomers on the surface to be coated, followed by UV or thermalcuring.

The second layer of the multi-layer barrier coating, an inorganicmaterial, may be formed over the first layer by radio frequencydischarge, direct or dual ion beam deposition, sputtering or plasmachemical vapor deposition, as described in U.S. Pat. Nos. 4,698,256,4,809,876, 4,992,298 and 5,055,318, the disclosures of which are hereinincorporated by reference.

For example, a method of depositing an oxide coating is provided byestablishing a glow discharge plasma in a previously evacuated chamber.The plasma is derived from one or more of the gas stream components, andpreferably is derived from the gas stream itself. The article ispositioned in the plasma, preferably adjacent the confined plasma, andthe gas stream is controllably flowed into the plasma. A silicon oxidebased film is deposited on the substrate to a desired thickness. Thethickness of the oxide coating is about 100 Angstroms (Å) to about10,000 Å. A thickness of less than about 5,000 Å may not providesufficient barrier and a thickness of greater than about 5,000 Å maycrack, thus decreasing the effective barrier. Most preferably, thethickness of the oxide coating is about 1,000 Å to about 3,000 Å.

Another method of depositing an oxide coating is by confining a plasmawith magnets. Preferably, the magnetically enhanced method fordepositing a silicon oxide based film on a substrate is preferablyconducted in a previously evacuated chamber of glow discharge from a gasstream. The gas stream preferably comprises at least two components: avolatilized organosilicon component, an oxidizer component such asoxygen, nitrous oxide, carbon dioxide or air and an optionally inert gascomponent.

Examples of suitable organosilicon compounds useful for the gas streamin the plasma deposition methods are liquid or gas at about ambienttemperature and when volatilized have a boiling point about 0° C. toabout 150° C. and include dimethysilane, trimethylsilane, diethylsilane,propylsilane, phenylsilane, hexamethyldisilane,1,1,2,2-tetramethyldisilane, bis (trimethylsilane)metlane, bis(dimethylsilyl) methane, hexamethyldisiloxane, vinyl trimethoxy silane,vinyl triethyoxysilane, ethylmethoxysilane, ethyltrimethoxysilane,divinyltetramethyldisiloxane, hexamethyldsilazanedivinyl-hexamethyltrisiloxane, trivinylpentamethyltrisiloxazane,tetraethoxysilane and tetramethoxysilane.

Among the preferred organo silicons are 1,1,3,3-tetramethyldisiloxane,trimethylsilane, hexamethyldisiloxane, vinyltrimethylsilane,methyltrimethoxysilane, vinyltrimethoxysilane and hexamethyldisilazane.These preferred organosilicon compounds have boiling points of 71° C.,55.5° C., 102° C., 123° C. and 127° C. respectively.

The optional inert gas of the gas stream preferably is helium, argon ornitrogen.

The volatilized organosilicon component is preferably admixed with theoxygen component and the inert gas component before being flowed intothe chamber. The quantities of these gases being so admixed arecontrolled by flow controllers so as to adjustably control the flow rateratio of the gas stream components.

Various optical methods known in the art may be used to determine thethickness of the deposited film while in the deposition chamber, or thefilm thickness can be determined after the article is removed from thedeposition chamber.

The deposition method of the present invention is preferably practicedat relatively high power and quite low pressure. A pressure less thanabout 500 millitorr (mTorr) should be maintained during the deposition,and preferably the chamber is at a pressure between about 43 to about490 millitorr during the deposition of film. Low system pressure resultsin lower deposition rates whereas higher system pressure provides fasterdeposition rates. When the plastic article to be coated is heatsensitive, a higher system pressure may be used to minimize the amountof heat the substrate is exposed to during deposition because highsubstrate temperatures are to be avoided for low Tg polymers such aspolypropylene and PET (Tg is -10° C. and 60° C. respectively).

The substrate is electrically isolated from the deposition system(except for electrical contact with the plasma) and is at a temperatureof less than about 80° C. during the depositing. That is, the substrateis not deliberately heated.

Referring to FIG. 6, the system for depositing a silicon oxide basedfilm comprises an enclosed reaction chamber 170 in which a plasma isformed and in which a substrate or tube 171, is placed for depositing athin film of material on a sample holder 172. The substrate can be anyvacuum compatible material, such as plastic. One or more gases aresupplied to the reaction chamber by a gas supply system 173. An electricfield is created by a power supply 174.

The reaction chamber can be of an appropriate type to perform any of theplasma-enhanced chemical vapor deposition (PECVD) or plasmapolymerization process. Furthermore, the reaction chamber may bemodified so that one or more articles may be coated with an oxide layersimultaneously within the chamber.

The pressure of the chamber is controlled by a mechanical pump 188connected to chamber 170 by a valve 190.

The tube to be coated is first loaded into chamber 170 in sample holder172. The pressure of the chamber is reduced to about 5 m Torr bymechanical pump 188. The operating pressure of the chamber is about 90to about 140 mTorr for a PECVD or plasma polymerization process and isachieved by flowing the process gases, oxygen and trimethyl silane, intothe chamber through monomer inlet 176.

The thin film is deposited on the outer surface of the tube and has adesired uniform thickness or the deposition process may be interruptedperiodically to minimize heating of the substrate and/or electrodesand/or physically remove particulate matter from the articles.

Magnets 196 and 198 are positioned behind electrode 200 to create anappropriate combination of magnetic and electrical fields in the plasmaregion around the tube

The system is suitable for low frequency operation. An example frequencyis 40 kHz. However, there can be some advantages from operating at amuch high frequency, such as in the radio frequency range of severalmegahertz.

The silicon oxide based film or blends thereof used in accordance withthis disclosure, may contain conventional additives and ingredientswhich do not adversely affect the properties of articles made therefrom.

The third layer of the multi-layer barrier coating may be formed on thesecond layer by dip-coating, roll-coating or spraying an aqueousemulsion of the PVDC homopolymer, followed by thermal curing.

The third layer may preferably be vinylidenechloride-acrylonitrile-methyl methacrylate-methyl acrylate-acrylic acidcopolymers, thermosetting epoxy coatings, parylene polymers, orpolyesters.

Preferably, the third layer is a parylene polymer. Parylene is thegeneric name for members of the polymer series developed by UnionCarbide Corporation. The base member of the series, called parylene N,is poly-p-exlylene, a linear, crystalline material: ##STR1##

Parylene C, a second member of the parylene series is produced from thesame monomer as parylene N and modified by the substitution of achlorine atom for one other aromatic hydrogens: ##STR2##

Parylene D, the third member of the parylene series is produced from thesame monomer as parylene N and modified by the substitution of thechlorine atom for two of the aromatic hydrogens: ##STR3##

Most preferably, the polymer layer is a vinylidene chloride-methylmethacrylate-methacrylate acrylic acid polymer (PVDC). This polymer isavailable as DARAN® 8600-C (trademark of W. R. Grace and Co.) sold byGRACE, Organic Chemicals Division, Lexington, Mass.

The third layer of the barrier coating, a polymer material, may be aparylene polymer applied to the second layer by a process similar tovacuum metallizing, as described in U.S. Pat. Nos. 3,342,754 and3,300,332, the disclosures of which are herein incorporated byreference. Alternatively, the third layer may be vinylidenechloride-acrylonitrile-methyl methacrylate-methyl acrylate-acid acrylicpolymer, applied to the second layer by dip-coating, roll-coating orspraying an aqueous emulsion of the polymer, followed by air drying ofthe coating, as described in U.S. Pat. Nos. 5,093,194 and 4,497,859, thedisclosure of which are herein incorporated by reference.

As shown in FIG. 7, the expoxide coating A and the silicon oxide basedcoating B may have defects or irregularities C. It is believed thatcomplete coverage of the substrate D cannot be achieved with only theexpoxide and silicon oxide based coatings. Therefore, a third coating ofPVDC, E is applied over the silicon oxide based coating to produce asubstantially complete barrier coating over the substrate surface.

A variety of substrates can be coated with a barrier coating by theprocess of the present invention Such substrates include, but are notlimited to packaging, containers, bottles, jars, tubes and medicaldevices.

A plastic blood collection tube coated with the multi-layer barriercoating will not interfere with testing and analysis that is typicallyperformed on blood in a tube. Such tests include but are not limited to,routine chemical analysis, biological inertness, hematology, bloodchemistry, blood typing, toxicology analysis or therapeutic drugmonitoring and other clinical tests involving body fluids. Furthermore,a plastic blood collection tube coated with the barrier coating iscapable of being subjected to automated machinery such as centrifugesand may be exposed to certain levels of radiation in the sterilizationprocess with substantially no change in optical or mechanical andfunctional properties.

A plastic blood collection tube coated with the multi-layer barriercoating is able to maintain 90% original draw volume over a period ofone year. Draw volume retention depends on the existence of a particlevacuum, or reduced pressure, inside the tube. The draw volume changes indirect proportion to the change in vacuum (reduced pressure). Therefore,draw volume retention is dependent on good vacuum retention. A plastictube coated with a barrier coating substantially prevents gas permeationthrough the tube material so as to maintain and enhance the vacuumretention and draw volume retention of the tube. Plastic tubes withoutthe multi-layer coating of the present invention may maintain about 90%draw volume for about 3 to 4 months.

If the multi-layer barrier coating is also coated or applied on theinner surface of the plastic blood collection tube, the barrier coatingmay be hemorepellent and/or have characteristics of a clot activator.

It will be understood that it makes no difference whether the plasticcomposite container is evacuated or not evacuated in accordance withthis invention. The presence of a barrier coating on the outer surfaceof the container has the effect of maintaining the general integrity ofthe container holding a sample so that it may be properly disposed ofwithout any contamination to the user. Notable is the clarity of thebarrier coating as coated or applied on the container and its abrasionand scratch resistance.

The barrier coating used in accordance with this disclosure, maycontainer conventional additives and ingredients which do not adverselyaffect the properties of articles made therefrom.

The following examples are not limited to any specific embodiment of theinvention, but are only exemplary.

EXAMPLE 1 METHOD FOR COATING PLASTIC SUBSTRATES TUBES WITH MULTI-LAYERBARRIER COATING

A polyamine--polyepoxide coating was made by reacting 7 moles oftetra-ethylene pentamine with 6 moles of EPON 828 polyepoxide in1-methoxy-2-propanol (Dowanol PM). To this mixture was added 21 g ofdiethanolamine, 36.1 g of N, N, N¹, N¹ tetrakis, (oxiranylmethyl-1,3-benzene dimethanamine, TETRAD X, Mitsubishi Gas Chemical Co.), 108.75grams of additional Dowanol PM, 111.18 g of 2-butoxyethanol and 6.7 g ofdeionized water. This mixture was applied to the substrate by dipping,spraying, or rolling the above described polyanine/polyepoxide mixtureonto the substrate and baked for 15-20 minutes at 68° C.

After aging for several days at ambient temperature, the substratecoated with the polyanine/polyepoxide mixture was then cleaned with amixture comprising equal parts of a micro detergent and de-ionized (DI)water solution. The substrate was rinsed thoroughly in DI water andallowed to air dry. The cleaned substrate was then stored in a vacuumoven at room temperature until it was to be coated.

The cleaned substrate was then attached to a holder which fits midwaybetween the electrodes in the glass vacuum chamber. The chamber wasclosed and a mechanical pump was used to achieve a base pressure of 5mTorr.

The electrode configuration is internally capacitively coupled withpermanent magnets on the backside of the titanium electrodes. Thisspecial configuration provides the ability to confine the glow betweenthe electrodes because of the increase in collision probability betweenelectrons and reacting gas molecules. The net result of applying amagnetic field is similar to increasing the power applied to theelectrodes, but without the disadvantages of higher bombardment energiesand increased substrate heating. The use of magnetron discharge allowsoperation in the low pressure region and a substantial increase inpolymer deposition rate

The monomer which consists of a mixture of trimethylsilane (TMS) andoxygen was introduced through stainless steel tubing near the electrodesThe gases were mixed in the monomer inlet line before introduction intothe chamber. Flow rates were manually controlled by stainless steelmetering valves. A power supply operating at an audio frequency of 40kHz was used to supply power to the electrodes. The system parametersused for thin film deposition of plasma polymerized TMS/O₂ on thepolymer substrate were as follows:

Surface Pretreatment: TMS Flow=0 sccm

Base Pressure=5 mTorr

Oxygen Flow=10 sccm

System Pressure=140 mTorr

Power=50 watts

Time=2 minutes

Oxide Deposition: TMS Flow=0.75-10 sccm

Oxygen Flow=2.5-3.0 sccm

System Pressure=90-100 mTorr

Power=30 watts

Deposition Time=5 minutes

After the thin film was deposited, the reactor was allowed to cool. Thereactor was then opened, and the substrate was removed.

A protective top coating of a water-based emulsion of PVDC copolymer wasapplied by dip coating and cured at 65° C. for about 10 minutes toproduce a final coating thickness averaging about 6 microns.

EXAMPLE 2 COMPARISON OF SUBSTRATES WITH AND WITHOUT MULTI-LAYER BARRIERCOATINGS

All of the substrates prepared in accordance with Examples 1 and 2 abovewere evaluated for oxygen permeance (OTR) in the oxide coatings asfollows.

(i) Oxygen permeance (OTR):

Film or plaque samples were tested for oxygen permeance (OTR) using a MOCON Ox-TRAN 2/20 (sold by Modem Controls, Inc., 7500 Boone Avenue N.,Minneapolis, Minn. 55428). A single side of the film sample was exposedto 1 atm of 100% oxygen atmosphere. Oxygen permeating through the samplefilm was entrained in a nitrogen carrier gas stream on the opposite sideof the film, and detected by a coulmetric sensor. An electrical signalwas produced in proportion to the amount of oxygen permeating throughthe sample. Samples were tested at 30° C. and 0% relative humidity(R.H.). Samples were conditioned for 1 to 20 hours prior to determiningoxygen permeance. The results are reported in Table 1 in units ofcc/m2-atm-day.

Tube samples were tested for oxygen permeance (OTR) using a MOCON O_(x)-TRAN 1,000 (sold by Modem Controls, Inc., 7500 Boone Avenue N.,Minneapolis, Minn. 55428). A package adapter was used for mounting thetubes in a manner that allowed the outside of the tube to be immersed ina 100% O₂ atmosphere while the inside of tube is flushed with a nitrogencarrier gas. The tubes were then tested at 20° C. and 50% R.H. The tubeswere allowed to equilibrate for 2-14 days before a steady statepermeability is determined. The results are reported in Table 1 in unitsof cc/m² -atm-day.

                  TABLE 1                                                         ______________________________________                                                        SiO.sub.x      Oxygen Transmission Rate                          Epoxide Coating PVDC (cc/m.sup.2 -atm-day)                                   Sample Coating Method Coating 30° C., 0% RH                          ______________________________________                                        PP tube,                                                                             no       no      no     60-70                                            control                                                                       PP tube no yes no 20-50                                                       PP tube yes no no 2.79                                                        PP tube yes yes no 0.58                                                       PP tube yes yes yes 0.15                                                      PP tube no no yes 15-30                                                     ______________________________________                                         Oxide Coatings = 1000-3000 Angstroms (as measured by Scanning Electron        Microscope)                                                                   PP = polypropylene                                                            tubes = nominal wall thickness of 40 mil                                 

What is claimed is:
 1. A multi-layer barrier coating comprising:a firstlayer comprising an epoxide material; a second layer on said first layercomprising a metal oxide; and a third layer on said second layercomprising an organic material.
 2. The coating of claim 1, wherein saidsecond layer is aluminum oxide or silicon oxide.
 3. The coating of claim1, wherein said third layer is polyvinylidene chloride.
 4. A method ofdepositing a multilayer barrier coating on a plastic substrate in apreviously evacuated chamber comprising:(a) applying an uncuredpolyamine polyepoxide mixture onto said plastic substrate; (b) curingsaid mixture; (c) vaporizing an organosilicon component and admixing thevolatilized organosilicon component with an oxidizer component andoptionally an inert gas component to form a gas steam exterior to thechamber; (d) establishing a glow discharge plasma in the chamber fromone or more of the gas stream components; (e) controllably flowing thegas stream into the plasma while confining at least a portion of theplasma therein; and (f) depositing a second layer of silicon oxideadjacent said first layer.
 5. The method of claim 4 furthercomprising:(g) dip coating a third layer of PVDC onto said second layer.6. The method of claim 4 wherein said first layer is pretreated byoxygen plasma.